Mercury switch construction



Feb. 25, 1964 c. A. ELLIS 3,122,621

MERCURY SWITCH CONSTRUCTION -Filed Nov. 20. 1961 I N VEN TOR. flzr/e i2?7/13 9%, f 74mm {ft/rags.

United States Patent 3,122,621 MERCURY SWETCH CSNSTRUCTKGN Chmies A.Ellis, Marion, Mass, assignor to Glass lite Industries, inc, Providence,R1, a corporation of Rhode island Filed Nov. 20, 1961, Ser. No. 153,5712 Claims. (fil. 200-152} The present invention relates to a liquidcontact switch. More particularly, the present invention relates to amercury-type switch that includes a rotatable capsule having separatedpools of mercury for making and breaking contact in an electricalcircuit.

The present application is a continuation-in-part of application SerialNo. 841,381, filed September 21, 1959. and entitled Mercury Switch, nowUS. Patent No. 3,045,088.

In the copending application, a mercury switch is disclosed thatincludes a unique capsule construction wherein normally separated poolsof mercury are brought into contact upon rotation of the capsule to themake or on position. The present invention includes structure similar tothat disclosed in the copending application and further incorporates afiller gas and a plated electrode to increase the elficiency of theswitch.

In some prior known mercury contact switches, a filler gas, such ashydrogen, has been used to fill the switch capsule in order to absorband dissipate the heat generated by the electrical are when the circuitthrough the mercury pool was completed. Hydrogen was employed as thefiller gas heretofore chiefly because of its high dielectric recoveryrate and good thermal characteristics. However, it has been found duringclosing of the circuit, the hydrogen filler tends to increase the arcingbetween the pools of mercury. Thus even with a very clean hydrogenfilled capsule, the high recovery rate of the hydrogen increases the areenergy between the mercury pools, and multiple interruptions will occuron make of the switch. These interruptions result from the explosivereaction that takes place between two spherical surfaces of mercury in ahydrogen atmosphere, and the initial high in-rush current under suchconditions tends to vaporize the mercury and thus separates the circuitwhich results in an arc. The specific heat characteristics and highthermal conductivity of hydrogen permits a rapid reestablishment ofcontact conditions, and the cycle is repeated until an interruptionoccurs at a suficiently low voltage that the resulting current is notefiective in initiating vaporization. As a result of the interruptionsor explosions, deposits form which tend to cause more and violentinterruptions during make of the circuit and thereby decrease theefiiciency of the switch.

It has been further discovered that the use of hydrogen as the gasfiller in a mercury switch capsule increases the switch resistance inthat the constant vaporization of the mercury at high temperatures andunder pressures greater than atmosphere gradually caused an amalgam ofmercury and hydrogen to form. This amalgam gradually increased inhydrogen content and eventually resulted in sluggishness of the mercury.As the mercury increased in sluggishness, the operating angle of thecapsule at which the switch established contact also increased andeventually resulted in a breakdown of the switch.

The present invention completely eliminates the use of hydrogen as thefiller gas in the mercury capsule and employs as the filler gas an inertgas such as argon. Argon, when utilized as the sole gas filler, has beenfound to eliminate the breakdowns in the switch occasioned by the use ofhydrogen since the thermal characteristics thereof provide areestablishment of the circuit more slowly than in the case of hydrogen.Moreover, since argon is inert, it will not form a compound with eitherthe electrodes, mercury or the casing of the capsule even when theswitch is subjected to severe operating conditions.

The mercury switch embodied herein further defines an improvement overthe prior known mercury switches in that it includes a nickel platedelectrode that extends into the mercury pool within the switch capsule.By nickel plating the electrode, an active electrode surface is producedwhich is easily wetted by the mercury thereby assuring a clean mercuryto mercury contact. Since nickel in itself is only very slightly solublein mercury, an oifensive amalgam will not be formed.

It is, therefore, an object of the present invention to provide anelectric switch utilizing a liquid contact circuit controller.

Another object of the present invention is to provide an electricmercury switch which includes a capsule having a well member positionedtherein for creating a mercury-to-mercury make or break action.

Still another object of the present invention is to provide a mercuryelectric switch which is positive in action and which includes a uniqueform of an electrode or contact member that cooperates with the wellmember within the capsule to close the circuit between the electricalcontacts of the switch.

Still another object of the invention is to provide a mercury switchhaving a capsule formed with an electrode extending outwardly therefromfor making electrical contact with a contact member.

Still another object is to provide a mercury switch that includes acapsule filled with an inert gas and operating with a mercury-to-mercurymake or break action.

Still another object is to provide an electric switch utilizing a liquidcontact circuit controller that includes a capsule filled with an inertgas such as argon.

Still another object is to provide a mercury switch including a capsulefilled with two separate pools of mercury, the pools uniting on make andseparating on break, and further including a nickel plated electrodethat extends into one of the mercury pools.

Still another object is to provide an electrode for use in a mercuryswitch that is nickel plated, thereby enabling better wetting of theelectrode with mercury, which in turn assures a clean mercury to mercurycontact during operation of the switch.

.Other objects, features and advantages of the invention will becomeapparent as the description thereof proceeds when considered inconnection with the accompanying illustrative drawings.

In the drawings which illustrate the best mode presently contemplatedfor carrying out the present invention:

FIG. 1 is a front elevational view of the electrical switch embodied inthe present invention;

FIG. 2 is a sectional view of the electric switch taken along lines 2-2in FIG. 1 and illustrating the on position of the switch;

FIG. 3 is a sectional view similar to FIG. 2, illustrating the switch inthe off position;

FIG. 4 is an enlarged view of the operating button and capsule assemblyshowing the mercury-to-mercury contact within the capsule well when theswitch is disposed in the on position;

FIG. 5 is an enlarged view of the operating button and capsule assemblysimilar to FIG. 4, showing the location of the mercury within thecapsule when the switch is disposed in the off position thereof;

FIG. 6 is a sectional view taken along line 6-6 of FIG. 4; and

FIG. 7 is a sectional view taken along lines 7-7 in FIG. 6.

Referring now to the drawing, FIGS. 1 through 3, the mercury switchembodied herein is generally indicated at 19 and includes a mountingstrap 12 having openings 14 formed at opposite ends thereof, theopenings 14 being adapted to receive a screw or other fastening element(not shown) for mounting the strap in position in a recess formed in awall or the like. The mounting strap 12 further includes a rectangularlyshaped opening in formedcentrally thereof which is adapted to receivetherethrough the operating button of the switch. Formed on the marginalportions defining the opening 16 are arcuate shaped portions 17 thatprovide for the movement of the operating button as will be describedhereinafter.

Secured to the mounting strap 12 by screws 18 which extend throughsuitable openings formed in the mounting strap is a body member 20, therearmost portion of which projects into the recess of the wall fixtureon which the switch is mounted. As shown in H6. 2, the body member Zilis formed in a shell construction, preferably of molded plastic, andincludes oppositely positioned outwardly extending recessed ears 22 and24 (FIG. 1). Formed in each of the ears 22, 24 is a recess 25 thatreceives a terminal screw 26 therein. The terminal screw 26 threadedlyextends through an opening formed in a contact head 28, the contact head28 being formed integral with a longitudinally extending contact member30. A contact member 32 (FIG. 6) is formed similarly to contact member39 and includes a contact head that receives a terminal screw that inturn extends into a recess formed in the car 24. It will be understoodthat contacts 30 and 32 are of identical construction except that theyare reversely disposed and extend adjacent opposite sides of body 20 sothat their respective contact heads can engage cars 22 and 24 in themanner indicated.

As shown in FIGS. 2 and 6, the contact members 30, 32 extendsubstantially the length of the interior of the body member 20- and arein spaced parallel relation with respect to each other. Enlarged centralportions 33 of the contact members are dished to define bearing surfacesfor rotatably receiving a capsule generally indicated at 34. The capsule34, which defines the liquid contact circuit controller of the subjectinvention, is formed in a generally tear-drop shape, as seen in crosssection in FIGS. 2 and 4, and includes a metallic cap 36 formed with aperipheral flange 38 (FIG. 6). Joined to the flange 33 as by welding orthe like and enclosing the cap as is a plate 4%) having a centralopening 42 formed therein. A seal 44 is positioned within the opening 42and is adapted to rigidly receive therethrough, in sealing relationtherewith, an arm of an electrode to be described hereinafter.

Located within the capsule 34 and positioned at the narrow portion ofthe tear-drop section is a well 46. The well 46 is formed of anon-metallic, non-corrosive material, such as ceramic, and includes achamber 48 in which a small pool of mercury 55} is disposed. The chamber48 is defined by a rear wall 51, side walls 52 and a relatively shortfront wall 53 formed with an inclined upper edge. The relatively shortfront wall '53 prevents the small pool of mercury '50 from fiowing outof the well in the off position of the switch, as shown in FIG. 5. Theside walls 52 of the well are positioned between the rear wall of thecap 36 and plate 4! and are spaced to define the chamber 48. The well ismaintained in position so that, as the capsule is rotated, the frontwall 53 will either extend above or below a pool of mercury 54 disposedwithin the capsule but outside the well. In the oif position of theswitch, the level of the larger or major body of mercury '54 disposedwithin the capsule 34 extends below the upper edge of the front wall 53;thus, the body of mercury '54 is prevented from communicating with thechamber 43 of the well 46 and the small pool of mercury 51 disposedtherein. As illustrated in FIG. 4, when the switch is moved to the onposition, the tear-drop shaped capsule is rotated clockwise, the narrowportion of the tear drop moving downwardly to cause the well 46 to betilted. in this position, since the surface of the body of mercury 54remains in a horizontal or level position, the level thereof wouldextend above the upper edge of the wall 53, and the mercury 54 thusflows over the inclined upper edge of the front wall 53 and into thechamber 48. The mercury thereby intermingles with the pool of mercury50, and a mercury-to-mercury contact between the body of mercury 54 andthe small pool of mercury 56- is effected. It is seen that the pools ofmercury 5h, '54 will be caused to communicate with each other with onlya slight rotary movement of the capsule 34, and in practice, the largepool of mercury will flow over the wall 53 after only a slight rotationof the capsule 34. In this connection, the sharp or inclined upper edgeof the front wall 53 provides for easier and faster makes and breaks ofthe switch ircuit. it has been found that in order to insure make orbreak with this relatively slight rotary movement of the capsule, theratio by volume of mercury 5t} should be greater than one to one.

In order to rotate the capsule 34, the capsule is formed with anoutwardly dished portion 56 on the bottom wall of the cup member 36, theoutwardly dished portion 56 making bearing contact with thecorresponding dished portion 33' of the contact element 32. An electrode58 is disposed within the chamber 43 of the Well 46, being spaced fromthe side walls 52 and extending upwardly therefrom. The chamber 48 isproportioned to easily accommodate the electrode 58 wherein the mercurycan more freely flow into the chamber 48 during the make operation. Theouter end of the electrode 58 is formed with an arm 60 that is joined tothe portion that extends within the well 46 at right angles with respectthereto, and another arm 62 of the electrode is joined to the arm 60 atright angles thereto, extending through the seal 44. The arm 62 has acontact button 64 secured to the end thereof which is formed with aconvex outer face that cooperates with the dished portion 33 of thecontact member 38. As illustrated in FIG. 6, the dished portion 56 andthe contact button 64 mount the capsule 34 for rotation between thecontact members 39 and 32. It will be understood that the securement offlange 38 to plate 40 effects an air-tight seal therebetween, while atthe same time the seal 44 is air tight, whereby the capsule is efi ectively hermetically sealed. This, of course, is important in mercuryswitches of this type in order to prevent undesirable oxidation of themercury and electrode.

The capsule 34 is adapted to be rotated in the body member 20 by anoperating button generally indicated at 70, the operating button '70including a handle portion 72 to which an arcuate shaped body 74 isintegrally joined. The underside of the body 74 is formed with arcuatesurfaces 76, 73 (FIG. 6) which are spaced apart to define an arcuateshaped groove therebetween, the groove 80 receiving the flange 38 of thecapsule 34 and the plate 40 therein. Joined to the sides of the body 74extending outwardly therefrom and following the arcuate configurationthereof are flanges 554, one of which is shown in FIGS. 2 and 4. Formedon the flanges 84 are projections 86 which, as shown in FIG. 2, in theassembled position of the switch are positioned within the arcuateportions 17 of the strap 12 and cooperate therewith to provide africtional force for stabilizing and maintaining the button in aselected position. The operating button 70 is adapted to positivelyengage the capsule 34 for imparting rotating movement thereto by meansof a projection 88 formed on the underside of the arcuate surface 76.The projection 83 extends into a recess 9t) formed in the wall of thecap 36 and, as seen in FIGS. 2 and 5, is held in snug engagement thereinby the frictional pressure between the projections 86 and the arcuateportions 17 of the strap 12. It is seen that rotation of the operate 54to pool.

ing button 70 will cause the capsule member 3'4 to rotate therewith, thelimit of movement being predetermined by the movement of the handleportion 72 of the operating button 7% within the switch cover plate (notshown).

In mercury switches of the type embodied herein, it is important toestablish immediate contact between the mercury and the electrode whenthe capsule is rotated to the on or make position. In some of the priorknown mercury switches, a gas filler, such as hydrogen, was introducedinto the capsule for the purpose of absorbing and dissipating heat thatresulted when the electrical circuit was established between the mercuryand electrode. It has been found that the use of a hydrogen fillerprevented instantaneous making between the mercury pool and theelectrode and that, moreover, multiple interruptions occurred on makingcontact, even with a very clean hydrogen-filled switch. This latterphenomenon is due to the explosive reaction that takes place when pointcontact is made between two spherical surfaces of mercury in a hydrogenatmosphere and when such surfaces are part of an electrical conductingcircuit. In order to eliminate the undesirable sparking resulting fromuse of a hydrogen atmosphere, an inert gas such as argon is employed asthe gas filler in the present invention and is introduced under pressureinto the capsule 34. Argon, when utilized as the sole gas filler,increases the emciency of the switch since in addition to its inertness,it has a relatively low capacity to conduct heat, thus resulting inlessening of the explosive efiect of the individual contacts. Argon alsotends to prevent reestablishment of a high voltage contact, therebypreventing interruptions when the capsule is moved to the make position,and, furdiermore, argon even under high temperature conditions is notcapable of forming an amalgam or a compound with the mercury orelectrode. As employed in the present invention, the argon filler isintroduced into the capsule in pure form and is maintained at a pressurenot below one atmosphere. Under operating conditions, it has been foundthat excellent results are produced by maintaining the pure argon in thecapsule at thirty p.s.i.

Argon used above as a filler gas is also beneficial in the interruptionof the electrical circuit in the switch. With an mgon atmospherecontained in the switch capsule as the sole gas filler, ionization ofthe mercury vapor is largely avoided, the argon acting to contaminatethe mercury vapor atmosphere on the occasions when it is copiouslyformed. in addition to this, when a high voltage is available, an argonglow discharge forms which has has a low current carrying capacity yetserves as a shunt resistance to limit the potential available forinitiating an arc.

Observation of the make and break events of the switch embodied hereinhave been made by use of a cathode ray oscilloscope, and in this studythe oscilloscope input was connected directly across the switch contactso that with the switch open a trace of line voltage was observed, andwith the switch closed a zero voltage horizontal trace was made.

The make event has three trace forms. If the circuit is completed on arising voltage but before the potential is great enough to start themercury vaporization, no instantaneous break follows, and the current isimmediateiy established. The same is true if the initial contact is in afalling voltage below the critical value. If, however, the contact ismade at any time above the critical voltage, the circuit is immediatelyinterrupted and the argon glow is formed. This persists until thevoltage falls to zero and the circuit is permanently established.

The break events are of a similar character except that the factor ofcontact separation is introduced. If slow separation of contacts takesplace, the traces on the oscilloscope are identical with the threeconditions described above for make. Where the circuit is opened at lowvoltage, either rising or falling, an immediate and permanentinterruption occurs. If the circuit is opened at a time when enoughpotential is available to start the argon glow, the glow will becontinuous until the next zero voltage is reached to accomplishpermanent interruption. However, if the separation of the contacts takesplace rapidly enough, a point is reached where the opening may be enoughto permit activation of the mercury. If the potential at this inst-antis also suflicient, a mercury arc can be formed which is extinguished asthe voltage passes through zero.

In contrast to the argon filler, a hydrogen filler, such as utilized inthe prior known switch constructions, causes rapid multipleinterruptions of the switch circuit, with reestablishing occurring manytimes during the half cycle voltage period. As indicated on theoscilloscope, the multiple interruptions produce a plurality ofsaw-tooth traces, each saw-tooth representing an explosion of mercurythat is quickly cooled by the presence of hydrogen.

As has hereinbefore been pointed out, the electrode 58 is coated with anickel plating 92 that results in better wettability of the electrode,thereby assuring a clean mercury-to-mercury contact. It should be noted,however, that in the normal manufacture of the switch 10 it is necessaryto pass the plated electrode together with the glass 44 and plate orheader 4% through the furnace in which the seal between these parts isbeing effected. Since this furnace pass would normally destroy theactive nickel surface, it is important that the furnace treatmentatmosphere be strongly reducing, such as by introducing a quantity' ofhydrogen, since a reducing atmosphere will not destroy the active nickelsurface. it has been found, however, that upon exposure to air thenickel plating is even more susceptible than usual to oxidizing in viewof this treatment in a reducing atmosphere, and hence it is essentialthat the cap 36 be assembled to the plate 40 as quickly as possibleafter the furnace sealing operation.

It will be understood that the better wettability of electrode 58 thatresults from nickel plating 92 enables contact to be made with a minimumthrow of the switch. In practice, it has been found that with anunplated electrode, the throw of the switch must be increased by as muchas 4 to 5 before contact is made. This is due to the fact that theabsence of plating 92 results in an electrode that has a tendency toresist wetting by the mercury, thus failing to achieve the cleanmercury-to-mercury contact which enables the switch to make morequickly.

It is also of importance to note that the corner 94 of side wall 52which abuts plate 40 overlaps and bears against a small portion of glassseal 44 (FIGS. 4-6). This is important in that when the plate 4%, seal44, well 46 and electrode 58 are passed through the furnace to effectthe seal between plate 49, seal 44 and electrode 53, the overlappingcorner 94 of well 46 will automatically fuse to glass seal 44 therebyholding the well 45 firmly in position, both during subsequent assemblyof cap 36 and operation of the completed switch.

In operation, when the mercury switch is located in the off position, asseen in FIG. -5, the handle portion 72 of the operating button 70 ispointing downwardly. In this position, the small pool of mercury 50 isprevented from making contact with the larger body of mercury 54 by thebarrier defined by the shortened wall 53 formed on the front of the well46. When the handle portion 72 is moved upwardly to the position shownin FIG. 4, the larger body of mercury 54 is caused to flow over the wall53 and into communication with the interior of the well 46, therebymaking contact with the small pool of mercury 59. Electrical contact isthereby established through the contact member 30, electrode 58, mercurybodies 50, 54, the cap 36 and the contact member 32. The inclined orpointed upper edge of wall 53 facilitates the make and break action ofthe switch during rotation thereof.

It is seen that the present invention provides a mercury switch that issimple in construction, etfective in operation, and inexpensive tomanufacture. The mercury-to-mercury make and break operation insures alonger life of the switch and provides for rapid make and break betweenthe contact elements. The argon filler eliminates the interruptionsnormally associated with gas fillers and tends to prevent oxidation,flaking and formation of undesirable compounds within the capsule. Theplating on the electrode within the capsule cooperates with the argonfiller to produce an active electrode surface that results in a decreaseof the throw angle of the switch and that generally increases theefficiency thereof.

'It will be obvious to those skilled in the art that various changes maybe made without departing from the spirit of the invention, andtherefore the invention is not limited to what is shown in the drawingsand described in the specifications, but only as indicated in theappended claims.

What is claimed is:

1. In an electric switch, a liquid contact circuit controller comprisinga hermetically sealed capsule constructed of conductive material, a wellformed of non-conductive material positioned within said capsule, a mainbody of conductive liquid located within said capsule adjacent to butoutside of said well, a secondary body of conductive liquid locatedWithin said Well, an electrode extending into said well into contactwith said secondary body and having a further portion extendingoutwardly through said capsule, and means insulating said electrode fromsaid capsule, said insulating means comprising a glass seal in the wallof said capsule through which said electrode extends whereby no contactis made between the electrode and the conductive capsule Wall, said wellhaving a portion in engagement with said glass seal and bonded theretoso as to maintain said well fixedly positioned within said capsule.

2. The switch of claim 1 further characterized in that said Well isceramic, the portion of said well which is in engagement with said glassseal being fused thereto in order to effect the aforesaid bondtherebetween.

References Cited in the file of this patent UNITED STATES PATENTS2,343,653 Finizio Mar. 7, 1944 2,417,764 Larson Mar. 18, 1947 2,916,589Cook et a1 Dec. 8, 1959 3,045,088 Ellis July 17, 1962

1. IN AN ELECTRIC SWITCH, A LIQUID CONTACT CIRCUIT CONTROLLER COMPRISINGA HERMETICALLY SEALED CAPSULE CONSTRUCTED OF CONDUCTIVE MATERIAL, A WELLFORMED OF NON-CONDUCTIVE MATERIAL POSITIONED WITHIN SAID CAPSULE, A MAINBODY OF CONDUCTIVE LIQUID LOCATED WITHIN SAID CAPSULE ADJACENT TO BUTOUTSIDE OF SAID WELL, A SECONDARY BODY OF CONDUCTIVE LIQUID LOCATEDWITHIN SAID WELL, AN ELECTRODE EXTENDING INTO SAID WELL INTO CONTACTWITH SAID SECONDARY BODY AND HAVING A FURTHER PORTION EXTENDINGOUTWARDLY THROUGH SAID CAPSULE, AND MEANS INSULATING SAID ELECTRODE FROMSAID CAPSULE, SAID INSULATING MEANS COMPRISING A GLASS SEAL IN THE WALLOF SAID CAPSULE THROUGH WHICH SAID ELECTRODE EXTENDS WHEREBY NO CONTACTIS MADE BETWEEN THE ELECTRODE AND THE CONDUCTIVE CAPSULE WALL, SAID WELLHAVING A PORTION IN ENGAGEMENT WITH SAID GLASS SEAL AND BONDED THERETOSO AS TO MAINTAIN SAID WELL FIXEDLY POSITIONED WITHIN SAID CAPSULE.